The formation of a variety of devices such as, for example, waveguides and semiconductors, typically includes one or more steps of etching the surface of a substrate which may be made of inorganic materials, such as, for example, SiO.sub.2, garnet and LiNbO.sub.3. Conventional etching techniques, such as masking a substrate with a patterned photoresist and then contacting the resulting patterned substrate with a chemical etchant to selectively dissolve material from the area defined by the pattern, present problems in controlling vertical and lateral penetration of the etchant into the substrate.
Some materials, such as for example, LiNbO.sub.3, are sufficiently resistant to chemical attack that they present the problem of finding a suitable mask or resist for the substrate which can withstand the chemicals which are used for etching.
In one method of overcoming this problem, the pattern to be etched is bombarded with ions in order to damage the patterned area. The resulting damaged area is etched with chemicals at a significantly greater rate than the remainder of the material. This technique of implanting ions within a material to be etched is disclosed, for example, in Johnson et al U.S. Pat. No. 3,808,068; Tefft et al U.S. Pat. No. 4,325,182; Aklufi U.S. Pat. No. 4,450,041; and, Jain et al U.S. Pat. No. 4,652,334. However, these processes, which use ions having a single incident energy, are capable of producing a sufficient level of damage only within a short distance from the surface.
In another method of providing patterns in chemically resistive material ions are impinged onto the patterned surface to erode material from the substrate; however, the mask used to define the pattern is subjected to the same erosive forces as the substrate material, and the erosion of the mask can diminish the lateral resolution of the desired pattern.